Processing of glass sheets usually involves heating such as for forming from a flat shape to a curved shape. See, for example, U.S. Pat. No. 7,958,750 Vild et al. and U.S. Pat. No. 8,132,428 Vild et al. During such processing, it is important for the hot glass sheets after heating to be accurately positioned so that the forming can be performed to a design shape such as when forming on a mold by gravity or between a pair of molds for press bending, etc. When heating of glass sheets prior to the forming is performed within a furnace on a roll conveyor, the location of the glass sheet has previously been sensed by a sensor along the direction of conveyance. However, during the heating conveyance, the glass sheet can rotate about a vertical axis and migrate laterally with respect to the direction of conveyance so that the actual glass position is not determined by the sensor. The rotation and lateral migration of the glass sheet during the heating can result from wear of the conveyor components, and conductive heat that is supplied by the conveyor rolls to the bottom surface of the glass sheet during the conveyance so as to provide increased heating relative to its top surface in a manner that causes the glass sheet to bow upwardly into an upwardly concave shape. Such an upwardly concave shape of the glass sheet causes its contact with the conveyor rolls to be more centrally located rather than evenly over a full flat surface, which causes the rotation and lateral migration. Furthermore, paint which is usually black, at the periphery of the glass sheet on its upper surface for use in current production vehicle glass can absorb additional heat but only at the periphery so that, combined with the roll heating of the lower surface, the glass sheet assumes a saddle shape that also can result in rotation and lateral migration of the glass from its intended path of travel.
Accurate lateral positioning which can also provide rotational positioning on a roll conveyor is disclosed by U.S. Pat. No. 4,282,026 McMaster et al. and utilizes sliding of the glass sheet on the conveyor rolls. Movement of conveyor rolls along the direction of conveyance to permit an upper vacuum platen to receive a glass sheet being conveyed without any relative movement along the direction of conveyance during the transfer is disclosed by U.S. Pat. No. 4,360,374 Nitschke; however, this approach does not correct rotational or lateral positioning.
All of the above patents and references cited therein are hereby incorporated by reference.